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xfs: improve handling of busy extents in the low-level allocator

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Currently we force the log and simply try again if we hit a busy extent,
but especially with online discard enabled it might take a while after
the log force for the busy extents to disappear, and we might have
already completed our second pass.

So instead we add a new waitqueue and a generation counter to the pag
structure so that we can do wakeups once we've removed busy extents,
and we replace the single retry with an unconditional one - after
all we hold the AGF buffer lock, so no other allocations or frees
can be racing with us in this AG.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Christoph Hellwig 2017-02-07 14:06:57 -08:00 committed by Darrick J. Wong
parent 5e30c23d13
commit ebf5587261
5 changed files with 166 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

93
fs/xfs/libxfs/xfs_alloc.c
View File

@ -221,20 +221,22 @@ xfs_alloc_get_rec(
* Compute aligned version of the found extent. * Compute aligned version of the found extent.
* Takes alignment and min length into account. * Takes alignment and min length into account.
*/ */
STATIC void STATIC bool
xfs_alloc_compute_aligned( xfs_alloc_compute_aligned(
xfs_alloc_arg_t *args, /* allocation argument structure */ xfs_alloc_arg_t *args, /* allocation argument structure */
xfs_agblock_t foundbno, /* starting block in found extent */ xfs_agblock_t foundbno, /* starting block in found extent */
xfs_extlen_t foundlen, /* length in found extent */ xfs_extlen_t foundlen, /* length in found extent */
xfs_agblock_t *resbno, /* result block number */ xfs_agblock_t *resbno, /* result block number */
xfs_extlen_t *reslen) /* result length */ xfs_extlen_t *reslen, /* result length */
unsigned *busy_gen)
{ {
xfs_agblock_t bno; xfs_agblock_t bno = foundbno;
xfs_extlen_t len; xfs_extlen_t len = foundlen;
xfs_extlen_t diff; xfs_extlen_t diff;
bool busy;
/* Trim busy sections out of found extent */ /* Trim busy sections out of found extent */
xfs_extent_busy_trim(args, foundbno, foundlen, &bno, &len); busy = xfs_extent_busy_trim(args, &bno, &len, busy_gen);
/* /*
* If we have a largish extent that happens to start before min_agbno, * If we have a largish extent that happens to start before min_agbno,
@ -259,6 +261,8 @@ xfs_alloc_compute_aligned(
*resbno = bno; *resbno = bno;
*reslen = len; *reslen = len;
} }
return busy;
} }
/* /*
@ -737,10 +741,11 @@ xfs_alloc_ag_vextent_exact(
int error; int error;
xfs_agblock_t fbno; /* start block of found extent */ xfs_agblock_t fbno; /* start block of found extent */
xfs_extlen_t flen; /* length of found extent */ xfs_extlen_t flen; /* length of found extent */
xfs_agblock_t tbno; /* start block of trimmed extent */ xfs_agblock_t tbno; /* start block of busy extent */
xfs_extlen_t tlen; /* length of trimmed extent */ xfs_extlen_t tlen; /* length of busy extent */
xfs_agblock_t tend; /* end block of trimmed extent */ xfs_agblock_t tend; /* end block of busy extent */
int i; /* success/failure of operation */ int i; /* success/failure of operation */
unsigned busy_gen;
ASSERT(args->alignment == 1); ASSERT(args->alignment == 1);
@ -773,7 +778,9 @@ xfs_alloc_ag_vextent_exact(
/* /*
* Check for overlapping busy extents. * Check for overlapping busy extents.
*/ */
xfs_extent_busy_trim(args, fbno, flen, &tbno, &tlen); tbno = fbno;
tlen = flen;
xfs_extent_busy_trim(args, &tbno, &tlen, &busy_gen);
/* /*
* Give up if the start of the extent is busy, or the freespace isn't * Give up if the start of the extent is busy, or the freespace isn't
@ -853,6 +860,7 @@ xfs_alloc_find_best_extent(
xfs_agblock_t sdiff; xfs_agblock_t sdiff;
int error; int error;
int i; int i;
unsigned busy_gen;
/* The good extent is perfect, no need to search. */ /* The good extent is perfect, no need to search. */
if (!gdiff) if (!gdiff)
@ -866,7 +874,8 @@ xfs_alloc_find_best_extent(
if (error) if (error)
goto error0; goto error0;
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
xfs_alloc_compute_aligned(args, *sbno, *slen, sbnoa, slena); xfs_alloc_compute_aligned(args, *sbno, *slen,
sbnoa, slena, &busy_gen);
/* /*
* The good extent is closer than this one. * The good extent is closer than this one.
@ -955,7 +964,8 @@ xfs_alloc_ag_vextent_near(
xfs_extlen_t ltlena; /* aligned ... */ xfs_extlen_t ltlena; /* aligned ... */
xfs_agblock_t ltnew; /* useful start bno of left side */ xfs_agblock_t ltnew; /* useful start bno of left side */
xfs_extlen_t rlen; /* length of returned extent */ xfs_extlen_t rlen; /* length of returned extent */
int forced = 0; bool busy;
unsigned busy_gen;
#ifdef DEBUG #ifdef DEBUG
/* /*
* Randomly don't execute the first algorithm. * Randomly don't execute the first algorithm.
@ -982,6 +992,7 @@ restart:
ltlen = 0; ltlen = 0;
gtlena = 0; gtlena = 0;
ltlena = 0; ltlena = 0;
busy = false;
/* /*
* Get a cursor for the by-size btree. * Get a cursor for the by-size btree.
@ -1064,8 +1075,8 @@ restart:
if ((error = xfs_alloc_get_rec(cnt_cur, &ltbno, &ltlen, &i))) if ((error = xfs_alloc_get_rec(cnt_cur, &ltbno, &ltlen, &i)))
goto error0; goto error0;
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
xfs_alloc_compute_aligned(args, ltbno, ltlen, busy = xfs_alloc_compute_aligned(args, ltbno, ltlen,
&ltbnoa, &ltlena); &ltbnoa, &ltlena, &busy_gen);
if (ltlena < args->minlen) if (ltlena < args->minlen)
continue; continue;
if (ltbnoa < args->min_agbno || ltbnoa > args->max_agbno) if (ltbnoa < args->min_agbno || ltbnoa > args->max_agbno)
@ -1183,8 +1194,8 @@ restart:
if ((error = xfs_alloc_get_rec(bno_cur_lt, &ltbno, &ltlen, &i))) if ((error = xfs_alloc_get_rec(bno_cur_lt, &ltbno, &ltlen, &i)))
goto error0; goto error0;
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
xfs_alloc_compute_aligned(args, ltbno, ltlen, busy |= xfs_alloc_compute_aligned(args, ltbno, ltlen,
&ltbnoa, &ltlena); &ltbnoa, &ltlena, &busy_gen);
if (ltlena >= args->minlen && ltbnoa >= args->min_agbno) if (ltlena >= args->minlen && ltbnoa >= args->min_agbno)
break; break;
if ((error = xfs_btree_decrement(bno_cur_lt, 0, &i))) if ((error = xfs_btree_decrement(bno_cur_lt, 0, &i)))
@ -1199,8 +1210,8 @@ restart:
if ((error = xfs_alloc_get_rec(bno_cur_gt, &gtbno, &gtlen, &i))) if ((error = xfs_alloc_get_rec(bno_cur_gt, &gtbno, &gtlen, &i)))
goto error0; goto error0;
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
xfs_alloc_compute_aligned(args, gtbno, gtlen, busy |= xfs_alloc_compute_aligned(args, gtbno, gtlen,
&gtbnoa, &gtlena); &gtbnoa, &gtlena, &busy_gen);
if (gtlena >= args->minlen && gtbnoa <= args->max_agbno) if (gtlena >= args->minlen && gtbnoa <= args->max_agbno)
break; break;
if ((error = xfs_btree_increment(bno_cur_gt, 0, &i))) if ((error = xfs_btree_increment(bno_cur_gt, 0, &i)))
@ -1261,9 +1272,9 @@ restart:
if (bno_cur_lt == NULL && bno_cur_gt == NULL) { if (bno_cur_lt == NULL && bno_cur_gt == NULL) {
xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR); xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
if (!forced++) { if (busy) {
trace_xfs_alloc_near_busy(args); trace_xfs_alloc_near_busy(args);
xfs_log_force(args->mp, XFS_LOG_SYNC); xfs_extent_busy_flush(args->mp, args->pag, busy_gen);
goto restart; goto restart;
} }
trace_xfs_alloc_size_neither(args); trace_xfs_alloc_size_neither(args);
@ -1344,7 +1355,8 @@ xfs_alloc_ag_vextent_size(
int i; /* temp status variable */ int i; /* temp status variable */
xfs_agblock_t rbno; /* returned block number */ xfs_agblock_t rbno; /* returned block number */
xfs_extlen_t rlen; /* length of returned extent */ xfs_extlen_t rlen; /* length of returned extent */
int forced = 0; bool busy;
unsigned busy_gen;
restart: restart:
/* /*
@ -1353,6 +1365,7 @@ restart:
cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp, cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
args->agno, XFS_BTNUM_CNT); args->agno, XFS_BTNUM_CNT);
bno_cur = NULL; bno_cur = NULL;
busy = false;
/* /*
* Look for an entry >= maxlen+alignment-1 blocks. * Look for an entry >= maxlen+alignment-1 blocks.
@ -1362,14 +1375,13 @@ restart:
goto error0; goto error0;
/* /*
* If none or we have busy extents that we cannot allocate from, then * If none then we have to settle for a smaller extent. In the case that
* we have to settle for a smaller extent. In the case that there are * there are no large extents, this will return the last entry in the
* no large extents, this will return the last entry in the tree unless * tree unless the tree is empty. In the case that there are only busy
* the tree is empty. In the case that there are only busy large * large extents, this will return the largest small extent unless there
* extents, this will return the largest small extent unless there
* are no smaller extents available. * are no smaller extents available.
*/ */
if (!i || forced > 1) { if (!i) {
error = xfs_alloc_ag_vextent_small(args, cnt_cur, error = xfs_alloc_ag_vextent_small(args, cnt_cur,
&fbno, &flen, &i); &fbno, &flen, &i);
if (error) if (error)
@ -1380,13 +1392,11 @@ restart:
return 0; return 0;
} }
ASSERT(i == 1); ASSERT(i == 1);
xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen); busy = xfs_alloc_compute_aligned(args, fbno, flen, &rbno,
&rlen, &busy_gen);
} else { } else {
/* /*
* Search for a non-busy extent that is large enough. * Search for a non-busy extent that is large enough.
* If we are at low space, don't check, or if we fall of
* the end of the btree, turn off the busy check and
* restart.
*/ */
for (;;) { for (;;) {
error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i); error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i);
@ -1394,8 +1404,8 @@ restart:
goto error0; goto error0;
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
xfs_alloc_compute_aligned(args, fbno, flen, busy = xfs_alloc_compute_aligned(args, fbno, flen,
&rbno, &rlen); &rbno, &rlen, &busy_gen);
if (rlen >= args->maxlen) if (rlen >= args->maxlen)
break; break;
@ -1407,18 +1417,13 @@ restart:
/* /*
* Our only valid extents must have been busy. * Our only valid extents must have been busy.
* Make it unbusy by forcing the log out and * Make it unbusy by forcing the log out and
* retrying. If we've been here before, forcing * retrying.
* the log isn't making the extents available,
* which means they have probably been freed in
* this transaction. In that case, we have to
* give up on them and we'll attempt a minlen
* allocation the next time around.
*/ */
xfs_btree_del_cursor(cnt_cur, xfs_btree_del_cursor(cnt_cur,
XFS_BTREE_NOERROR); XFS_BTREE_NOERROR);
trace_xfs_alloc_size_busy(args); trace_xfs_alloc_size_busy(args);
if (!forced++) xfs_extent_busy_flush(args->mp,
xfs_log_force(args->mp, XFS_LOG_SYNC); args->pag, busy_gen);
goto restart; goto restart;
} }
} }
@ -1454,8 +1459,8 @@ restart:
XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0); XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
if (flen < bestrlen) if (flen < bestrlen)
break; break;
xfs_alloc_compute_aligned(args, fbno, flen, busy = xfs_alloc_compute_aligned(args, fbno, flen,
&rbno, &rlen); &rbno, &rlen, &busy_gen);
rlen = XFS_EXTLEN_MIN(args->maxlen, rlen); rlen = XFS_EXTLEN_MIN(args->maxlen, rlen);
XFS_WANT_CORRUPTED_GOTO(args->mp, rlen == 0 || XFS_WANT_CORRUPTED_GOTO(args->mp, rlen == 0 ||
(rlen <= flen && rbno + rlen <= fbno + flen), (rlen <= flen && rbno + rlen <= fbno + flen),
@ -1484,10 +1489,10 @@ restart:
*/ */
args->len = rlen; args->len = rlen;
if (rlen < args->minlen) { if (rlen < args->minlen) {
if (!forced++) { if (busy) {
xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR); xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
trace_xfs_alloc_size_busy(args); trace_xfs_alloc_size_busy(args);
xfs_log_force(args->mp, XFS_LOG_SYNC); xfs_extent_busy_flush(args->mp, args->pag, busy_gen);
goto restart; goto restart;
} }
goto out_nominleft; goto out_nominleft;

125
fs/xfs/xfs_extent_busy.c
View File

@ -334,25 +334,31 @@ restart:
* subset of the extent that is not busy. If *rlen is smaller than * subset of the extent that is not busy. If *rlen is smaller than
* args->minlen no suitable extent could be found, and the higher level * args->minlen no suitable extent could be found, and the higher level
* code needs to force out the log and retry the allocation. * code needs to force out the log and retry the allocation.
*
* Return the current busy generation for the AG if the extent is busy. This
* value can be used to wait for at least one of the currently busy extents
* to be cleared. Note that the busy list is not guaranteed to be empty after
* the gen is woken. The state of a specific extent must always be confirmed
* with another call to xfs_extent_busy_trim() before it can be used.
*/ */
void bool
xfs_extent_busy_trim( xfs_extent_busy_trim(
struct xfs_alloc_arg *args, struct xfs_alloc_arg *args,
xfs_agblock_t bno, xfs_agblock_t *bno,
xfs_extlen_t len, xfs_extlen_t *len,
xfs_agblock_t *rbno, unsigned *busy_gen)
xfs_extlen_t *rlen)
{ {
xfs_agblock_t fbno; xfs_agblock_t fbno;
xfs_extlen_t flen; xfs_extlen_t flen;
struct rb_node *rbp; struct rb_node *rbp;
bool ret = false;
ASSERT(len > 0); ASSERT(len > 0);
spin_lock(&args->pag->pagb_lock); spin_lock(&args->pag->pagb_lock);
restart: restart:
fbno = bno; fbno = *bno;
flen = len; flen = *len;
rbp = args->pag->pagb_tree.rb_node; rbp = args->pag->pagb_tree.rb_node;
while (rbp && flen >= args->minlen) { while (rbp && flen >= args->minlen) {
struct xfs_extent_busy *busyp = struct xfs_extent_busy *busyp =
@ -504,24 +510,25 @@ restart:
flen = fend - fbno; flen = fend - fbno;
} }
spin_unlock(&args->pag->pagb_lock); out:
if (fbno != bno || flen != len) { if (fbno != *bno || flen != *len) {
trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len, trace_xfs_extent_busy_trim(args->mp, args->agno, *bno, *len,
fbno, flen); fbno, flen);
*bno = fbno;
*len = flen;
*busy_gen = args->pag->pagb_gen;
ret = true;
} }
*rbno = fbno; spin_unlock(&args->pag->pagb_lock);
*rlen = flen; return ret;
return;
fail: fail:
/* /*
* Return a zero extent length as failure indications. All callers * Return a zero extent length as failure indications. All callers
* re-check if the trimmed extent satisfies the minlen requirement. * re-check if the trimmed extent satisfies the minlen requirement.
*/ */
spin_unlock(&args->pag->pagb_lock); flen = 0;
trace_xfs_extent_busy_trim(args->mp, args->agno, bno, len, fbno, 0); goto out;
*rbno = fbno;
*rlen = 0;
} }
STATIC void STATIC void
@ -540,6 +547,21 @@ xfs_extent_busy_clear_one(
kmem_free(busyp); kmem_free(busyp);
} }
static void
xfs_extent_busy_put_pag(
struct xfs_perag *pag,
bool wakeup)
__releases(pag->pagb_lock)
{
if (wakeup) {
pag->pagb_gen++;
wake_up_all(&pag->pagb_wait);
}
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
}
/* /*
* Remove all extents on the passed in list from the busy extents tree. * Remove all extents on the passed in list from the busy extents tree.
* If do_discard is set skip extents that need to be discarded, and mark * If do_discard is set skip extents that need to be discarded, and mark
@ -554,27 +576,76 @@ xfs_extent_busy_clear(
struct xfs_extent_busy *busyp, *n; struct xfs_extent_busy *busyp, *n;
struct xfs_perag *pag = NULL; struct xfs_perag *pag = NULL;
xfs_agnumber_t agno = NULLAGNUMBER; xfs_agnumber_t agno = NULLAGNUMBER;
bool wakeup = false;
list_for_each_entry_safe(busyp, n, list, list) { list_for_each_entry_safe(busyp, n, list, list) {
if (busyp->agno != agno) { if (busyp->agno != agno) {
if (pag) { if (pag)
spin_unlock(&pag->pagb_lock); xfs_extent_busy_put_pag(pag, wakeup);
xfs_perag_put(pag);
}
pag = xfs_perag_get(mp, busyp->agno);
spin_lock(&pag->pagb_lock);
agno = busyp->agno; agno = busyp->agno;
pag = xfs_perag_get(mp, agno);
spin_lock(&pag->pagb_lock);
wakeup = false;
} }
if (do_discard && busyp->length && if (do_discard && busyp->length &&
!(busyp->flags & XFS_EXTENT_BUSY_SKIP_DISCARD)) !(busyp->flags & XFS_EXTENT_BUSY_SKIP_DISCARD)) {
busyp->flags = XFS_EXTENT_BUSY_DISCARDED; busyp->flags = XFS_EXTENT_BUSY_DISCARDED;
else } else {
xfs_extent_busy_clear_one(mp, pag, busyp); xfs_extent_busy_clear_one(mp, pag, busyp);
wakeup = true;
}
} }
if (pag) { if (pag)
spin_unlock(&pag->pagb_lock); xfs_extent_busy_put_pag(pag, wakeup);
}
/*
* Flush out all busy extents for this AG.
*/
void
xfs_extent_busy_flush(
struct xfs_mount *mp,
struct xfs_perag *pag,
unsigned busy_gen)
{
DEFINE_WAIT (wait);
int log_flushed = 0, error;
trace_xfs_log_force(mp, 0, _THIS_IP_);
error = _xfs_log_force(mp, XFS_LOG_SYNC, &log_flushed);
if (error)
return;
do {
prepare_to_wait(&pag->pagb_wait, &wait, TASK_KILLABLE);
if (busy_gen != READ_ONCE(pag->pagb_gen))
break;
schedule();
} while (1);
finish_wait(&pag->pagb_wait, &wait);
}
void
xfs_extent_busy_wait_all(
struct xfs_mount *mp)
{
DEFINE_WAIT (wait);
xfs_agnumber_t agno;
for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
struct xfs_perag *pag = xfs_perag_get(mp, agno);
do {
prepare_to_wait(&pag->pagb_wait, &wait, TASK_KILLABLE);
if (RB_EMPTY_ROOT(&pag->pagb_tree))
break;
schedule();
} while (1);
finish_wait(&pag->pagb_wait, &wait);
xfs_perag_put(pag); xfs_perag_put(pag);
} }
} }

11
fs/xfs/xfs_extent_busy.h
View File

@ -58,9 +58,16 @@ void
xfs_extent_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno, xfs_extent_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno,
xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata); xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata);
bool
xfs_extent_busy_trim(struct xfs_alloc_arg *args, xfs_agblock_t *bno,
xfs_extlen_t *len, unsigned *busy_gen);
void void
xfs_extent_busy_trim(struct xfs_alloc_arg *args, xfs_agblock_t bno, xfs_extent_busy_flush(struct xfs_mount *mp, struct xfs_perag *pag,
xfs_extlen_t len, xfs_agblock_t *rbno, xfs_extlen_t *rlen); unsigned busy_gen);
void
xfs_extent_busy_wait_all(struct xfs_mount *mp);
int int
xfs_extent_busy_ag_cmp(void *priv, struct list_head *a, struct list_head *b); xfs_extent_busy_ag_cmp(void *priv, struct list_head *a, struct list_head *b);

8
fs/xfs/xfs_mount.c
View File

@ -45,6 +45,7 @@
#include "xfs_rmap_btree.h" #include "xfs_rmap_btree.h"
#include "xfs_refcount_btree.h" #include "xfs_refcount_btree.h"
#include "xfs_reflink.h" #include "xfs_reflink.h"
#include "xfs_extent_busy.h"
static DEFINE_MUTEX(xfs_uuid_table_mutex); static DEFINE_MUTEX(xfs_uuid_table_mutex);
@ -213,6 +214,7 @@ xfs_initialize_perag(
INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC); INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
if (xfs_buf_hash_init(pag)) if (xfs_buf_hash_init(pag))
goto out_free_pag; goto out_free_pag;
init_waitqueue_head(&pag->pagb_wait);
if (radix_tree_preload(GFP_NOFS)) if (radix_tree_preload(GFP_NOFS))
goto out_hash_destroy; goto out_hash_destroy;
@ -1078,6 +1080,12 @@ xfs_unmountfs(
*/ */
xfs_log_force(mp, XFS_LOG_SYNC); xfs_log_force(mp, XFS_LOG_SYNC);
/*
* Wait for all busy extents to be freed, including completion of
* any discard operation.
*/
xfs_extent_busy_wait_all(mp);
/* /*
* We now need to tell the world we are unmounting. This will allow * We now need to tell the world we are unmounting. This will allow
* us to detect that the filesystem is going away and we should error * us to detect that the filesystem is going away and we should error

2
fs/xfs/xfs_mount.h
View File

@ -384,6 +384,8 @@ typedef struct xfs_perag {
xfs_agino_t pagl_rightrec; xfs_agino_t pagl_rightrec;
spinlock_t pagb_lock; /* lock for pagb_tree */ spinlock_t pagb_lock; /* lock for pagb_tree */
struct rb_root pagb_tree; /* ordered tree of busy extents */ struct rb_root pagb_tree; /* ordered tree of busy extents */
unsigned int pagb_gen; /* generation count for pagb_tree */
wait_queue_head_t pagb_wait; /* woken when pagb_gen changes */
atomic_t pagf_fstrms; /* # of filestreams active in this AG */ atomic_t pagf_fstrms; /* # of filestreams active in this AG */